When colour printing is carried out by any form of print engine (including laser copiers, ink jet printers and dye transfer printers) there is no guarantee that the colour output will necessarily achieve the correct effect. Colour adjustment within the print engine may therefore be needed and an experienced operator can , after suitable trial and error, achieve an acceptable output. There is however no standard method for adjusting the colour output. Furthermore the input image might be in the form of a flat copy scanned by a copier or in the form of a digital file in a computerised print engine.